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Date: Wed, 11 Nov 2015 02:36:43 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Måns Rullgård <mans@...sr.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
netdev <netdev@...r.kernel.org>, slash.tmp@...e.fr
Subject: Re: [PATCH v5] net: ethernet: add driver for Aurora VLSI NB8800
Ethernet controller
On Wed, Nov 11, 2015 at 1:07 AM, Måns Rullgård <mans@...sr.com> wrote:
> Andy Shevchenko <andy.shevchenko@...il.com> writes:
>>>>> + nb8800_writel(priv, NB8800_TX_DESC_ADDR, txb->dma_desc);
>>>>> + wmb(); /* ensure desc addr is written before starting DMA */
>>>>
>>>> Hm… Have I missed corresponding rmb() ? If it's about MMIO, perhaps mmiowb() ?
>>>
>>> Possibly.
>>
>> Standalone wmb() doesn't make sense.
>
> It does if you need to enforce ordering between normal and I/O memory.
> In fact, since the descriptor is filled in using normal memory accesses,
> my understanding is that mmiowb() would be insufficient here. The
> comment could be improved, however.
Can you then explain what exactly you are assured against in all cases
where you are using wmb()s? It seems I don't recognize this part in
some excerpts.
--
With Best Regards,
Andy Shevchenko
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